1. Field of the Invention
This invention relates to a water-soluble lubricant for warm or hot metal forming, and more particularly to a water-soluble lubricant for warm or hot metal forming that is fed between a die and a workpiece; possesses excellent lubricity for reducing the friction therebetween, or excellent release properties for reducing the contact time; has less of an adverse effect on the operating environment and operating efficiency; and can be readily treated as wastewater after use.
The water-soluble lubricant for warm or hot metal forming can be used for forging, extrusion, pressing, wiring drawings, and other types of metal forming in warm or hot regions.
2. Description of the Prior Art
Lubricants are conventionally used in metal forming with the aim of reducing the friction between metal materials and tools or dies, to further smooth the metal forming, and to facilitate the cooling and protection of tools or metals and the release of metal materials from the tools or dies. Examples of such lubricants include graphite lubricants, which are obtained by dispersing graphite powder in oil or water. Graphite lubricants have excellent lubricity and release properties, and are therefore widely used in the metal-forming field.
Graphite lubricants are disadvantageous, however, in the sense that there is a risk that the graphite powder will scatter or deposit on the machinery during application, and will have an adverse effect on the operating environment. Another feature of a graphite lubricant is that the graphite powder plugs the pipes or nozzles coated with the lubricant, and impedes operations as the number of usage cycles increases. Additional work is also needed for cleaning. A resulting drawback is that the operating efficiency of metal forming is markedly reduced. In addition, a graphite lubricant contains graphite powder and is therefore technically difficult to treat as wastewater, and is commonly disposed of by incineration or landfill. In view of this, graphite-free lubricants devoid of graphite powder are needed in order to address the problems of such graphite lubricants.
From this perspective, silicate lubricants and carboxylic acid lubricants have been developed as graphite-free lubricants. A silicate lubricant (JP-A-59-64698) comprising, for example, phosphoric acid, a phosphate, and alkali metal salts of silicic and boric acids is known as one example. Also, known examples of carboxylic acid lubricants include adipates and organic thickeners (JP-A-55-139498), organic thickeners and alkali metal salts of phthalic acid (JP-A-58-84898), alkali metal salts of aromatic carboxylic acids (JP-A-60-1293), organic thickeners and alkali metal salts of maleic acid (JP-A-61-103996), organic thickeners and alkali metal salts of fumaric acid (JP-A-58-52395), alkali salts of aromatic polycarboxylic acids (JP-A-62-50396), alkali metal salts or alkaline-earth metal salts of ligninsulfonic acid (JP-A-62-64698), and polycarboxylic acid reaction products of trimellitic acid and alkali metal hydroxides or alkaline-earth metal hydroxides (JP-A-63-89592).
However, such silicate lubricants tend to deposit nonvolatile lubricant components or mixed accretions comprising the nonvolatile lubricant components and metal abrasion powder in the concavities or corner portions of dies. As a result, underfills are apt to form in a plastically worked product. In addition, lubricants comprising carboxylates and organic thickeners, while devoid of problems associated with the deposition of matter on dies and the adverse effect on the operating environment or operating efficiency, are still inferior to graphite lubricants in terms of lubricity and release properties. Another drawback is that the combined use of thickeners in the lubricants comprising carboxylates and organic thickeners increases the viscosity of these lubricants and, as a result, reduces die life due to a reduction in cooling properties and an increase in the die temperature (increase in the die temperature in the steady state maintained during continuous working).
Furthermore, a reduction in the ability of a lubricant to be treated by flocculation is disadvantageous in that the lubricant cannot be discharged into the environment because of the increased COD value following a wastewater treatment. Since laws and regulations related to environmental protection are believed to become even more stringent in the future, there is currently an urgent need for lubricants that can be readily treated as wastewater.